1. Field of the Invention
The present invention relates to a toner for developing an electrostatic image by an image forming method such as electrophotography and electrostatic printing, or a toner for forming a toner image in a toner jet image forming method.
2. Description of the Related Art
Recently, due to demands for higher-speed and highly stable printers and copiers, faster charge control and charge characteristic that is less susceptible to environmental changes have been required. To control the charge characteristic of a toner, a charge control agent is added. Especially, due to reasons such as consideration of the environment, demands for a more stable charge characteristic, and production costs, the use of a resin (charge control resin) having a charge control function as a toner raw material has been proposed. Japanese Patent Nos. 2694572 and 2807795 propose a toner that contains a copolymer containing a salicylic acid group, and a toner that contains a styrene resin and a copolymer containing a sulfonic acid group as a charge control resin. Further, Japanese Patent Application Laid-Open Nos. 2003-96170 and 2003-215853 propose a PES charge control resin formed by polycondensation of a monomer containing a sulfonic acid (salt) as a resin having improved compatibility with a binder resin.
However, although toners such as those described above has good charge rise, deterioration in the toner development characteristic due to overcharging of the toner and unevenness in the toner charge distribution is a problem. Such a problem is especially noticeable after many sheets have been printed using the toner.
It is an object of the present invention to provide a toner which has excellent charge rise and charge stability, and which has a sharp charge distribution even after prolonged use.